# Low-mass White Dwarfs with Hydrogen Envelopes as a Missing Link in the Tidal Disruption Menu

## TL;DR

This paper explores how low-mass white dwarfs with hydrogen envelopes can produce bright, rapid flares when tidally disrupted by intermediate-mass black holes, offering new insights into black hole populations and disruption dynamics.

## Contribution

It introduces a new class of tidal disruption events involving low-mass white dwarfs with hydrogen envelopes, highlighting their role as probes of intermediate-mass black holes and disruption hydrodynamics.

## Key findings

- Disruption of low-mass white dwarfs can produce brighter, faster flares than typical TDEs.
- Hydrogen-rich fallback can explain rapid nuclear transients like Dougie and PTF10iya.
- White dwarf disruptions probe black holes in the $10^5$ to $10^7$ solar mass range.

## Abstract

We construct a menu of objects that can give rise to bright flares when disrupted by massive black holes (BHs), ranging from planets to evolved stars. Through their tidal disruption, main sequence and evolved stars can effectively probe the existence of otherwise quiescent supermassive BHs and white dwarfs can probe intermediate mass BHs. Many low-mass white dwarfs possess extended hydrogen envelopes, which allow for the production of prompt flares in disruptive encounters with moderately massive BHs of $10^5$ to $10^7~M_\odot$--masses that may constitute the majority of massive BHs by number. These objects are a missing link in two ways: (1) for probing moderately massive BHs and (2) for understanding the hydrodynamics of the disruption of objects with tenuous envelopes. A flare arising from the tidal disruption of a $0.17~M_\odot$ white dwarf by a $10^5~M_\odot$ BH reaches a maximum between 0.6 and 11 days, with a peak fallback rate that is usually super-Eddington and results in a flare that is likely brighter than a typical tidal disruption event. Encounters stripping only the envelope can provide hydrogen-only fallback, while encounters disrupting the core evolve from H- to He-rich fallback. While most tidal disruption candidates observed thus far are consistent with the disruptions of main sequence stars, the rapid timescales of nuclear transients such as Dougie and PTF10iya are naturally explained by the disruption of low-mass white dwarfs. As the number of observed flares continues to increase, the menu presented here will be essential for characterizing nuclear BHs and their environments through tidal disruptions.